Induction hardening is a non-contact heat treatment process which utilizes the phenomena of inductive heating to harden all or a portion of a surface layer of a workpiece. During this process, the conductive workpiece is placed into a strong alternating magnetic current, thereby creating electrical currents on the surface of the workpiece. These electrical currents flow predominantly into the surface layer of the workpiece causing this layer to rapidly increase in temperature.
In the context of a steel workpiece, ideally the same is heated until the surface layer is at a temperature that is at or above the transformation range temperature. Thereafter, the workpiece is immediately quenched thereby forming a martensitic structure in the surface layer that is harder than the base material. Generally, the hardened surface layer functions as a protective “skin” for the workpiece, with reduced wear vulnerability. The aforementioned process is used in various applications, including tool tip hardening, pin and shaft hardening, blade edge hardening, etc.
There are generally two principal methods for induction edge hardening. The first is referred to as “single shot” hardening, wherein a workpiece is held statically in the alternating magnetic field so that the entire area that will be heat treated is heated simultaneously. The second method is referred to as “traverse” hardening, wherein the workpiece moves through the alternating magnetic field progressively, so that the area that will be heat treated is incrementally heated as it passes through the field.
In either case, both single shot and traverse edge hardening processes are known to produce substantial deformations in the workpiece. As a result, a post-hardening straightening operation is required to remove the dimensional anomalies that result from these deformations to ensure that the workpiece meets its required dimensional specifications.
Unfortunately, such a post-hardening straightening process is very undesirable. From a cost perspective, this additional process increases the cost of manufacturing per part. From a lead time perspective, this additional process increases the overall processing time from order to delivery. Furthermore, the depth of the surface layer that is hardened must be deep enough to accommodate subsequent material removal during straightening. As such, the heat treated surface layer is often times much deeper than necessary simply to ensure that a sufficient amount of the hardened surface layer will remain. To achieve this overshoot in hardened depth, higher frequency and power requirements are necessary during the induction edge hardening process to generate a sufficient amount of electrical current that will achieve the desired hardened surface layer depth.
Therefore, there is a need in the art for an edge hardening apparatus and method that will substantially reduce or entirely eliminate the need for any post-hardening straightening operations. The invention provides such an apparatus and method. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.